1. Field of the Invention
The invention relates to the process of designing and fabricating semiconductor chips. More specifically, the invention relates to a method and an apparatus for generating an optical proximity correction (OPC) segmentation based on modeled intensity gradients, wherein the OPC segmentation is used by an OPC process to generate corrections for the layout of an integrated circuit so that the layout prints more accurately on a semiconductor chip.
2. Related Art
As integration densities on a semiconductor chips continue to increase at an exponential rate, it is becoming progressively harder to deal with optical effects that arise during the optical lithography process involved in manufacturing the semiconductor chips. These optical effects can cause unwanted distortions in the printed layout that is generated by the optical lithography process.
To remedy this problem, a layout is often subjected to a model-based optical proximity correction (OPC) operation, which adjusts the layout to compensate for optical effects. (Although the term “optical proximity correction” is used in this specification, more generally the term as used herein refers to correction for any specified proximity effects, e.g. optical, micro-loading, etch, resist, etc.) These adjustments are made based upon results of model-based simulations of the printed layout. During this OPC operation, edges in the layout are divided into segments, and each segment is adjusted with a negative or a positive bias based upon a deviation between the desired layout and the simulated layout.
One of the most effective techniques to increase OPC correction accuracy is to reduce the length of the correction segment, thereby allowing finer manipulation units for the final correction. This approach leads to correction improvements, but also leads to data volume explosion and increases mask construction difficulties. These construction difficulties can lead to masks that cannot be inspected, and sometimes not even constructed. (Note that the term “mask” as used in this specification is meant to include the term “reticle.”).
Current methodologies for determining OPC model-based segment sizes are based on worst-case correction scenarios, combined with rules that look at pattern placement to choose locations where larger than worst-case segment lengths may be used. These tools have been effective means of sampling and correcting patterns at 130 nm and above, but at 90 nm and below, some segment lengths need to be as small as 25% to 20% of the wavelength of the radiation (or light) used in the exposure of the mask to produce adequate process margin and correction, e.g. for λ=193 nm, this would imply ˜38-49 nm segments. Segment lengths in these ranges can produce regions on the mask that cannot be inspected nor sometimes constructed. These mask construction issues effectively prevent the use of the very short segments necessary to make high-precision corrections.
Hence, what is needed is a method and an apparatus that facilitates using very short segment lengths without the above-described problems.